Semiconductor devices including gallium oxide (Ga2O3), which has a large band gap, are receiving attention as next-generation switching devices capable of achieving high voltage, low loss, and high heat resistance. Such semiconductor devices are expected to be applied to power semiconductor apparatuses, such as inverters. Also, thanks to their wide band gaps, these semiconductor devices are expected to be applied to light-receiving/emitting devices, such as LEDs and sensors. According to Non-Patent Literature 1 (Kentaro Kaneko, “Growth and Physical Properties of Corundum-Structured Gallium Oxide-Based Mixed Crystal Thin Film,” Kyoto University doctoral dissertation, March, 2013), the band gaps of mixed crystals formed by mixing indium or aluminum or both with gallium oxide can be controlled, and such mixed crystals form an extremely attractive material system as InAlGaO-based semiconductors. As used herein, InAlGaO-based semiconductors refer to InXAlYGaZO3 (0≦X≦2, 0≦Y≦2, 0≦Z≦2, X+Y+Z=1.5 to 2.5) semiconductors and can be regarded as a system of materials each containing gallium oxide.